Here's why:
* "Avail" usually means to be of use or benefit. It's often used in the phrase "of no avail" (meaning useless or ineffective).
* "Avail yourself of something" means to take advantage of an opportunity.
Here are some correct ways to phrase your request:
* "Please make yourself available for an urgent meeting."
* "Please attend an urgent meeting."
* "Please be present for an urgent meeting."
Let me know if you need more help with this or any other wording!